This invention relates to electro-optical readers and more particularly to correlation circuits for use in bar code readers.
There has recently developed a need to quickly and accurately identify an object for purposes of location, sortation and routing. For example, with the ever increasing volume of letter mail there is a need for rapid and accurate mechanical identification and sorting to insure rapid and accurate mail delivery. Document identification and sortation is also becoming a significant problem in many industries such as banking and insurance wherein a significant volume of paper work must be processed daily on a reliable basis. The quick and accurate interpretation of data manifestations has also become important in fields where returnable media are utilized, such as the moving stock of railroads. Also, in the warehousing industry there is developing a need to quickly and accurately identify the location of stored items for retrieval thereof.
Commonly, the objects mentioned above are encoded in an optically-sensible bar code that requires appropriate code recognition equipment for the interpretation thereof.
Various systems are available for applying coded data to a document such as standard bar code printers and ink jet printers. The quality of such printing varies considerably such that in the worst case and under high magnification the coded data appears like a random splattering of ink droplets. The many methods and means for applying the coded data to carriers, together with the working environments to which the data bearing carriers are subject, provide a myriad of sources which have a degrading effect on the quality and readability of the encoded data. Those sources provide data bearing carriers having low print-contrast ratio, low reflectance of envelopes, poor bar print quality, bar to bar variation in quality, contrast and spacing, and voids within the bars as well as extraneous ink between bars. Most prior art code readers have had a common disadvantage in that they are not effective to consistantly and accurately translate encoded data of a substandard quality.